Studio bosses have given early approval for two sequels to the Transformers remake due out in July.

Director Michael Bay has also told how his version of the 1980s cartoon classic is heavy on the special effects and has cost some £50 million.

A trailer of the movie, to be released next month after several delays, is said to demonstrate impressive CGI as the Autobots go head-to-head in battle with the Decepticons.

Bay said he thought the combination of human actors and heavy effects had paid off. "It's got a lot of action, but at the same time it's very funny and it's got heart," he explained. "I only wanted to do Transformers if I could do it realistically."

Meanwhile, the DreamWorks studio has given the provisional go-ahead for two more movies.